BlockSign
VerifySign up
v0.1 · live on solanaopen beta

BlockSign emits a tamper-evident proof on Solana every time a document changes hands. Cryptographic, not photographic. Verifiable by anyone, forever.

Sign up free →See how it worksemail + password — no wallet
Avg finality
0.0s
Avg fee / sig
0.000001SOL
Launch
May 2026
Network
SOLANA
blocksign.ink/sign/0xa1f7…
ready
Agreement · 02 of 03 pages

Mutual Non-Disclosure Agreement

SHA-256 · b3a1…f72c

This Agreement is entered into by Northwind Labs, Inc. and Halcyon Capital LLC as of the date last signed below.

Each party agrees to maintain the confidentiality of disclosed materials for a term of 24 months, consistent with the standards in §3.

HC
Counterparty
Halcyon Capital9pQr…vN3k
awaiting…
NW
You
Northwind Labs7Hk2…aQ9F
your turn →
tx → pending
Features

Built for signatures that hold up in court — and on-chain.

[01]

Cryptographic, not photographic

A wet signature scan proves nothing. We commit a SHA-256 of the PDF's content to Solana inside an obfuscated stamp. The math is the receipt.

[02]

No accounts to lose

Email & password to sign in. Counterparties just click a link.

[03]

Verifiable by anyone, forever

Drop a signed PDF into the public verifier; the proof is portable, the chain is permanent.

[04]

Sub-second finality

412ms

Solana settles in under half a second for a fraction of a cent.

[05]

Multi-signer by default

Add as many signers as the document needs. Set a deadline; each signed version emits its own memo on chain.

[06]

Audit trail by default

Every signed version is its own memo tx. The full version history is a chain of transaction signatures anyone can replay.

How it works

Three steps from PDF to proof.

Step 01

Upload your PDF

Drop a contract, NDA, or offer letter. We compute the SHA-256 server-side and store the file behind row-level access — the content never reaches our analytics.

Step 02

Send to signers

Add signer emails. Each signer gets a single-use, token-gated link — they click, sign in the browser, done. No wallet, no signup, no SOL needed.

Step 03

Commit & verify

Each signed version emits a Solana memo carrying the document's stamp. Anyone holding the PDF can verify it against chain state, with or without a BlockSign account.

Architecture

How the proof flows.

  1. PDFupload · server-side
    01
  2. SHA-2563 digests · base64
    02
  3. STAMPv0 · obfuscated
    03
  4. SOLANAmemo · server payer
    04
STAMPED PDFtx sig · receipt
VERIFIERre-hash · match chain
on-chain commitderived artifactv0:<obfuscated stamp> · <1000 byte memo · ~412ms finality
On-chain proof

Every signed document carries its own receipt.

Don't trust us. Verify the chain.

Every BlockSign document produces a portable receipt. Hand the PDF to a counterparty, a court, or an auditor — they can verify authenticity independently, with or without our app online.

  • SHA-256 document hash committed to Solana every signed version
  • Each signed version recorded as a separate on-chain memo transaction
  • Tamper-evident: a single byte change invalidates the document hash
  • Free verifier on this site — no BlockSign account required
  • Or run the open-source verifier yourself — audit the algorithm end-to-end
Audit the verifier on GitHub
Certificate of signature
v1
DocumentMutual NDA — Northwind × Halcyon
SHA-256
Signer 17Hk2…aQ9F · Northwind Labs
tx
at2026-04-25T14:22:08Z
Signer 29pQr…vN3k · Halcyon Capital
tx
at2026-04-25T14:24:31Z
finalizedblock 287,449,102
Sealed
Comparison

Faster, cheaper, and provable.Wet signatures rely on intent. DocuSign relies on a vendor. BlockSign relies on math — a hash committed to a public chain that anyone can re-derive and re-verify, long after the contract is filed away.

Cost per signature
BlockSign
$0.0008
DocuSign
$0.40 – $3.00
Wet signatures
$5 – $25
Finality
BlockSign
412ms
DocuSign
seconds
Wet signatures
days
Proof you can verify
BlockSign
yes
DocuSign
no
Wet signatures
no
Tamper-evident
BlockSign
yes
DocuSign
partial
Wet signatures
no
Works if vendor disappears
BlockSign
yes
DocuSign
no
Wet signatures
n/a
Counterparty signup
BlockSign
click a link
DocuSign
account + email
Wet signatures
in person
Open-source verifier
BlockSign
yes
DocuSign
no
Wet signatures
n/a